Long Term Evolution (LTE) uses Licensed Assisted Access (LAA) to perform carrier aggregation between a primary cell (PCell) and one or more lower power, secondary cells (SCells). The PCell operates in licensed spectrum, whereas with LAA the SCells operate in unlicensed spectrum for offloading in order to improve throughput.
Discovery Reference Signals (DRS) improve a wireless device's discovery of different cells in heterogeneous networks. The wireless device adjusts the AGC gain for SCells based on a DRS received in the prior DRS Measurement Timing Configuration (DMTC) as compared with data. Prior to transmission, a wireless device or a secondary cell performs a Listen Before Talk (LBT) procedure to ensure that the unlicensed spectrum is not already occupied. If the unlicensed spectrum is occupied, discontinuous transmission on the SCells makes it infeasible to guarantee successful DRS transmission for AGC gain adjustment at every DRS occasion. As a result, if there is an LBT failure, meaning the unlicensed channel is occupied, more than one DRS period (e.g., 40 ms, 80 ms, 160 ms . . . ) is needed for an AGC gain adjustment.